Basically your configuration looks ok. And the fact, that you get the response from http://jetons-hp:2030/elfinder.connector suggests that HttpHandler is correctly configured. I'm guessing that problem is somewhere in the html/js or authentication.
Could you verify that generated url in:

is exactly the same as http://jetons-hp:2030/elfinder.connector? Also did you check what request is being made and which server error occurs in some developer's tool (personally I like Chrome's dev tools the best)?

You have configured "Windows Authentication" in a web.config - could you check what happens if you change it to "Forms authentication"?

Ok, I don't know how I missed it earlier, but you are using ASPX view engine or just WebForms, so you can't use @Url.Content(...) because this structure exists only in Razor view engine. Instead just type: